The present invention relates generally to a damping spacer for overhead conductor bundles, and particularly to a compact damping spacer that has no central frame, is economical to manufacture, is light in weight and requires a minimum of parts and material.
There are presently available a large variety of devices for spacing overhead, parallel conductors and for damping vibrations and oscillations of such conductors. However, all of these devices have certain disadvantages that the damping spacer of the present invention does not have. Many of the presently available damping spacers, for example, employ a central frame on which conductor clamps are mounted, as a part of the structure designed to effect spacing of the conductors, and stop or motion limiting structures associated with the frame and clamps for protecting damping elements of the spacer from excessive forces tha may be encountered in overhead bundle conductors. The clamps of these devices usually have relatively short arms, and are often connected to the frame only through the agency of the damping elements so that the damping elements are required to support the weight of the frame. This tends to reduce the life and damping efficiency of the damping elements.
The use of a frame and motion limiting structures is also costly in that the components involved, and the process of assembling them, involve costs that are reflected in the ultimate selling price of the spacer. Further, the short arms of the clamps do not provide a sufficiently effective lever for working rather stiff, higher tensile strength damping elements that are employed because of their higher strength and longer life characteristics. Such elements require high thresholds of vibration energy before damping action is initiated in comparison to softer, shorter lived damping devices.
A further disadvantage of the frame type of spacer is the fact that the mass and weight of the frame add to the overall weight of the spacer, which weight must be borne by the conductors to which the spacer is attached. Also, the additional weight involves additional cost in the process of shipping and transporting such spacers.
Examples of damping spacers employing a central frame and relatively short clamp arms are shown in U.S. Pat. Nos. 3,083,258; 3,443,019; 3,474,184; 3,613,104; 3,748,370 and 3,777,047. Examples of spacers in which damping elements support the weight of a frame are shown in the above U.S. Pat. Nos. 3,083,258; 3,443,019; 3,748,370; 3,777,047, as well as in U.S. Pat. Nos. 3,582,983; 3,617,609 and 3,702,371.
Another problem encountered with certain of the presently available damping spacers is the inability of the arms of the spacers to return to their original, normal position after the arms are moved in response to conductor motion. The large power authorities, such as the Tennessee Valley and Bonneville Power Authorities, generally require that the spacer arms of a spacer return to a normal position under their own effort. Damping spacers using friction discs as the damping elements, for example, either depend upon the return movement of the conductors, to return the spacer arms to their normal, original position, or a spring element is required to return the arms. Further, a spring element is required to compensate for wear of the friction discs. A damping spacer using such friction discs and spring elements is shown in U.S. Pat. No. 3,474,184, listed above. In FIGS. 4 and 5 of British Patent No. 1,084,102, a damping spacer is shown in which friction discs are used without a spring element to return the spacer arms to a normal position. Spring elements, however, are used to preload the friction discs against the arms of the spacer in the British patent.
Another disadvantage of the presently available and prior devices for spacing conductors is the inability of these devices to insure spacing of the conductors under severe, short circuit conditions. Short circuits on a conductor bundle involve flows of heavy current through the conductors that generate a corresponding strong magnetic field component that directs the conductors rapidly inwardly in a straight line toward the geometric center of the bundle, and thus toward each other. Unless a rigid spacing structure is provided to directly resist these forces, the conductors will come together and become entangled with one another.
A central, rigid frame, used in the type of spacer discussed above, is helpful in this regard but suffers from the disadvantages of frame type spacers outlined above. U. S. Pat. No. 3,230,295 shows a conductor spacing device that would function as an effective spacer under short circuit conditions, if constructed of suitably rigid, high strength materials, but the device is not an effective damper of conductor vibration or oscillation since it does not employ a mechanism that is capable of dissipating the energy of such vibration or oscillation in any significant manner.
A further problem with certain, presently available damping spacers is the heavy stresses and cycling imposed upon the damping elements of the spacers by "articulation" of the spacer within a bundle of conductors. Individual conductors in a span of a conductor bundle tend to move relative to one another in a lengthwise or longitudinal direction of the conductors due to unequal contraction and stretching of the conductors, and due to the wind blowing across the conductors at velocities that bow the conductors in the direction of the wind by different amounts. These relative conductor movements and bows are large and thus cause any spacers clamped to the conductors to articulate within the bundle by corresponding large amounts. If the clamps clamping the spacer in the bundle are connected to a frame of the spacer through the agency of the damping elements, the damping elements are heavily worked and stressed by such articulation, such heavy working greatly shortening the life of the damping elements. This is true even when resilient bushings are employed between the spacer clamps and the conductors. In order for such bushings to effectively protect the damping elements from such articulating movements, and the resulting heavy stresses, the bushings would have to be soft to the point that they would not effectively grip the conductor. Examples of damping spacers in which the damping elements of the spacers would be unprotected from such articulation stresses are shown in the above-listed U.S. Pat Nos. 3,582,983 and 3,702,371. An example of a spacer particularly designed to provide articulation movements within the spacer is shown in U.S. Pat. No. 3,263,021. Such a structure, however, provides little or no damping of conductor vibration or oscillation.
Another problem associated with certain, presently available damping spacers is the general inefficiency of the mechanism associated with the spacers that provides the damping function. For example, the damping means associated with frame type spacers generally work independently of each other in damping vibration of one conductor of a bundle of conductors so that only one damping element is operable to dampen the vibration, the other elements remaining inactive and unused.